The moon phase display is a valued function in watchmaking, which complicates the manufacture of the movement, and which soon occupies a large volume inside the case. It is not always easy to correct such a display.
EP Patent Application No 2853957A1 in the name of CHRISTOPHE CLARET discloses a moon phase display mechanism which includes two discs rotating at different speeds, one of which bears the depiction of the moon and the other includes several apertures, arranged to reveal the depiction of the moon on the first disc to indicate in series the moon phases of a lunation through one of the apertures, and which are separated by several moon covers, which are all simultaneously visible. The moon phases of the successive lunations are indicated through adjacent apertures.
US Patent Application No 2006/2217771 in the name of ZIMMERMANN discloses a moon phase mechanism which includes a moon disc secured in a concentric manner on a moon display disc, wherein the moon disc is secured such that the moon disc rotates with respect to the moon display disc during the normal activity of the mechanism, The moon display disc is in a stationary position during the normal activity of the device, and is arranged to move only for manual display modifications.